Mycophenolate mofetil (RS-61443), the morpholino-ethyl ester of mycophenolic acid (MPA) is being evaluated as an immunosuppressant for use following solid organ transplantation. MPA is a potent and specific inhibitor of de novo purine synthesis and blocks the proliferation of both T and B lymphocytes. This is a non-randomized, multicenter 3-year open-label study of oral myophenolate mofetil as an immunosuppressant in pediatric patients receiving renal and hepatic allografts.